Preheat oven to 400. Roast sweet potatoes on a baking sheet in oven until soft, about 30-45 mins. Poke with knife to ascertain doneness. Let cool, peel, & mash in a large bowl. Whisk together the eggs, sugar, spices, salt, lemon zest & cream in a bowl. Add to sweet potatoes & mix thoroughly. Don’t overmix , as there should be some texture to the potatoes, though not necessarily lumps. Add butter & mix well. Pour into pie crust & bake for 45-55 mins until a knife inserted into the center comes out clean. Cool completely before serving. If you like, garnish with whipped cream.